Name the steps necessary to perform a Gram Stain correct answers 1. Allow sample to dry
2. Heatfix sample using incinerator for 30-60 second
3. Flood with crystal violet and let it sit for one minute- rinse well with water
4. Flood with iodine and let sit for one minute - rinse well with water
...
MBI 405 Lab Midterm || All Correct.
Name the steps necessary to perform a Gram Stain correct answers 1. Allow sample to dry
2. Heatfix sample using incinerator for 30-60 second
3. Flood with crystal violet and let it sit for one minute- rinse well with water
4. Flood with iodine and let sit for one minute - rinse well with water
5. Flood with decolorizer until the liquid flowing off the slide become clear - rinse well with
water
6. Flood with safranin and let sit for one minute - rinse well with water
Normal Flora: why is it important, what is found in general areas of the body, etc. correct
answers Most common areas: oral cavity, nasopharyngeal mucosa, and the skin.
Orapharyngeal: streptococci (alpha-hemolytic strep), diptheroids, non-pathogenic neisseria spp.,
mycoplasmas, spirochetes, and anaerobes.
Nasal: staphylococci (coagulase-negative staph), S. aureus, diphtheroid
Skin: staph (coagulase negative), S. aureus, diphtheroid, propionibacteria.
Diagnostic Methods: pharyngeal swabs are normally used to diagnose pharyngitis, nasal swabs
are often used to detect carriers of MRSA, skins swabs can be used to test for vancomycin-
resistant enterococcus (VRE).
Normal flora is important because it offers colonization resistance (pathogenic bacteria cannot
bind in already bound spaces) and the bacteria perform an array of function to assist in
metabolism and other bodily processes.
Staphylococci correct answers Short chain or grape-like clusters. Catalase positive. Facultative
anaerobes. Found in soil and on skin and mucosa of humans. Typical pathogens encountered in
clinical setting (S. aureus distinguished from other staph because its coagulase positive, part of
group coagulase-positive staph (CPS))
S. saprophyticus differentiated from S. epidermidis because saphro is resistant to antibiotic
novobiocin
Micrococci correct answers Pairs, tetrads, or irregular clusters.
Catalase positive.
Strict aerobes
Found in soil and on skin and mucosa of humans.
Saprophytes, usually non-pathogenic but can be opportunistic (micrococcus luteus)
Streptococcus correct answers Gram positive. Usually arranged in chains in broth - can also be
single or diplococci. Catalase negative (differentiates staphs from streps).
Aerotolerant anaerobes.
Homolactic fermenters.
Strep species are differentiated by hemolysis (those that do beta hemolysis either a result of
streptolysin O or Streptolysin S. O = oxygen labile, does not function in presence of O2. S =
oxygen stable. Majority of strep is beta-hemolytic)
, Classified using lancefield antigen classification: cell-wall compositions (viridians streptococcus:
alpha hemolytic streptococci such as Streptococcus bovis and Streptococcus salivarius)
Streptococcus pneumoniae correct answers Not grouped for same reasons as viridians Strep.
Alpah hemolytic
Senstiive to optochin
soluble in bile
Group A: Strep pyogenes correct answers Beta-hemolytic
Found in human nasopharynx and skin
Produce SLO and SLS exotoxins
Bacitracin sensitive
Group B: strep agalactiae correct answers Beta-hemolytic
Found in female genital tract
Bacitracin resistance
CAMP factor positive
Group C: strep equi, strep equisimilis correct answers Beta hemolytic
Found as pathogens in horses and cattle
Can be transferred to humans
Commercial source of streptokinase (used to treat thromboses)
Enterococcus correct answers Normal flora on skin and mucosa membrane of urogenital and GI
tracts.
Alpha or gamma hemolytic.
Hydrolyze esculin as C source.
Can grow on bile salts and at 45 C.
Considered group D strep until 1984.
Enzymes produces by Staphs (catalase, coagulase) correct answers Catalase test: smear colony
onto slide and add H2O2 - positive result is bubbles.
Coagulase test: inoculate tube of plasma - plasma is solidified for positive result
Streps (SLS, SLO, CAMP factor) correct answers CAMP factor: enhances beta-hemolytic effect
of S. aureus when in close contact; produces arrowhead shape on BAP (S. pyogenes is negative,
S. agalactiae is positive)
SLS: Streptolysin S - Stable in oxygenic conditions -> hemolysin should occur on surface of
agar.
SLO: oxygen labile streptolysin -> hemolysis will only occur if the plate is stabbed so as to allow
an anaerobic pocket to form
Three types of hemolysis and what they look like on blood agar plates correct answers Alpha:
greenish color of streak, think lining of hemolysis surrounding the colonies.
Beta: complete clearing of blood around streak
Gamma: no hemolysis present
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